Methods and apparatuses for producing laminated glass sheets

ABSTRACT

According to one embodiment, a method for forming a laminated glass sheet includes forming a multi-layer glass melt from a molten core glass and at least one molten cladding glass. The multi-layer glass melt has a width W m , a melt thickness T m  and a core to cladding thickness ratio T c :T cl . The multi-layer glass melt is directed onto the surface of a molten metal bath contained in a float tank. The width W m  of the multi-layer glass melt is less than the width W f  of the float tank prior to the multi-layer glass melt entering the float tank. The multi-layer glass melt flows over the surface of the molten metal bath such that the width W m  of the multi-layer glass melt increases, the melt thickness T m  decreases, and the core to cladding thickness ratio T c :T cl remains constant as the multi-layer glass melt solidifies into a laminated glass sheet.

This application is a divisional of U.S. application Ser. No. 14/413,625filed on Jan. 8, 2015, which claims the benefit of priority under 35U.S.C. §371 of International Application Number PCT/IB2012/001715 filedon Jul. 13, 2012, the content of each of which is relied upon andincorporated herein by reference in its entirety.

BACKGROUND

Field

The present specification generally relates to laminated glass sheetsand, more specifically, to methods and apparatuses for producinglaminated glass sheets by float processes.

Technical Background

Glass articles, such as cover glasses, glass backplanes and the like,are employed in both consumer and commercial electronic devices such asLCD and LED displays, computer monitors, automated teller machines(ATMs) and the like. Some of these glass articles may include “touch”functionality which necessitates that the glass article be contacted byvarious objects including a user's fingers and/or stylus devices and, assuch, the glass must be sufficiently robust to endure regular contactwithout damage. The glass articles incorporated in these devices may besusceptible to damage during transport and/or use of the associateddevice. Accordingly, glass articles used in such devices may requireenhanced strength to be able to withstand not only routine “touch”contact from actual use, but also incidental contact and impacts.

Various processes may be used to strengthen glass articles, includingchemical tempering and thermal tempering. Chemical and thermal temperingprocesses may be used to strengthen a glass article after the article isformed, thereby requiring additional processing steps and handling ofthe glass article, both of which may result in damage to the glassarticle which increases production costs and decreases productivity,particularly for larger glass articles.

Accordingly, a need exists for alternative methods and apparatuses forforming strengthened glass sheets.

SUMMARY

According to one set of embodiments, a method for forming a laminatedglass sheet may include forming a multi-layer glass melt from a moltencore glass and at least one molten cladding glass. The multi-layer glassmelt may have a width W_(m), a melt thickness T_(m) and a core tocladding thickness ratio T_(c):T_(cl). The multi-layer glass melt may bedirected onto the surface of a molten metal bath contained in a floattank having a width W_(f). The width W_(m) of the multi-layer glass meltis less than the width W_(f) of the float tank prior to the multi-layerglass melt entering the float tank. The multi-layer glass melt may flowover the surface of the molten metal bath such that the width W_(m) ofthe multi-layer glass melt increases, the melt thickness T_(m)decreases, and the core to cladding thickness ratio T_(c):T_(cl) remainsconstant as the multi-layer glass melt solidifies into a laminated glasssheet.

In another set of embodiments, a method for forming a laminated glasssheet may include forming a molten core glass from a core glasscomposition and forming a molten cladding glass from a cladding glasscomposition. A slot draw apparatus comprising a core glass slot and atleast one cladding glass slot may be provided. The core glass slot andthe at least one cladding glass slot may be oriented in parallel withone another. The slot draw apparatus may be positioned over a float tankcontaining a molten metal bath and oriented at a slot angle greater thanor equal to 0° and less than 90° with respect to a surface of the moltenmetal bath. A width W_(s) of the slot draw apparatus may be less than awidth W_(f) of the float tank. The molten core glass and the moltencladding glass may be delivered to the slot draw apparatus such that themolten core glass passes through the core glass slot and the moltencladding glass passes through the at least one cladding glass slot. Themolten cladding glass and the molten core glass may form a multi-layerglass melt with a width W_(m), a melt thickness T_(m), and a core tocladding thickness ratio T_(c):T_(cl) upon exiting the slot drawapparatus. The width W_(m) of the multi-layer glass melt is less thanthe width W_(f) of the float tank. The multi-layer glass melt may bedirected onto the surface of the molten metal bath. As the multi-layerglass melt flows over the surface of the molten metal bath, the widthW_(m) of the multi-layer glass melt increases, the melt thickness T_(m)decreases, and the core to cladding thickness ratio T_(c):T_(cl) remainsconstant as the multi-layer glass melt solidifies into a laminated glasssheet.

In yet another set of embodiments, an apparatus for forming a laminatedglass sheet may include a core glass melting vessel, a cladding glassmelting vessel and a slot draw apparatus comprising a core glass slotand at least one cladding glass slot. The core glass slot and the atleast one cladding glass slot may be oriented in parallel with oneanother. The core glass slot may be fluidly coupled to the core glassmelting vessel such that molten core glass can be delivered from thecore glass melting vessel to the core glass slot. The at least onecladding glass slot may be fluidly coupled to the cladding glass meltingvessel such that molten cladding glass can be delivered from thecladding glass melting vessel to the at least one cladding glass slot.The apparatus may further include a float tank containing a molten metalbath. The float tank may have a width W_(f) which is greater than awidth W_(s) of the slot draw apparatus. The slot draw apparatus may bepositioned over the float tank and oriented at a slot angle greater thanor equal to 0° and less than 90° with respect to a surface of the moltenmetal bath.

Additional features and advantages of the methods and apparatuses forforming laminated glass sheets will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from that description or recognized by practicing theembodiments described herein, including the detailed description whichfollows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description describe various embodiments and areintended to provide an overview or framework for understanding thenature and character of the claimed subject matter. The accompanyingdrawings are included to provide a further understanding of the variousembodiments, and are incorporated into and constitute a part of thisspecification. The drawings illustrate the various embodiments describedherein, and together with the description serve to explain theprinciples and operations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A schematically depicts an exemplary glass manufacturing apparatusfor forming laminated glass sheets, according to one or more embodimentsshown and described herein;

FIG. 1B schematically depicts a portion of the glass manufacturingapparatus of FIG. 1A;

FIG. 2 schematically depicts a top view of the glass manufacturingapparatus of FIG. 1A;

FIG. 3 schematically depicts a front view of a slot draw apparatus forforming a multi-layer glass melt;

FIG. 4 schematically depicts a cross section of the slot draw apparatusof FIG. 3; and

FIG. 5 schematically depicts a cross section of a multi-layer glass meltaccording to one or more embodiments shown and described herein.

DETAILED DESCRIPTION

Reference will now be made in detail to methods and apparatuses forforming laminated glass sheets, embodiments of which are schematicallydepicted in the accompanying drawings. Whenever possible, the samereference numerals are used throughout the drawings to refer to the sameor like parts. One embodiment of a method for forming a laminated glasssheet is schematically depicted in FIG. 1A. The method generallyincludes forming a multi-layer glass melt from a molten core glass andat least one molten cladding glass. The multi-layer glass melt may havea width W_(m), a melt thickness T_(m) and a core to cladding thicknessratio T_(c):T_(cl). The multi-layer glass melt may be directed onto thesurface of a molten metal bath contained in a float tank having a widthW_(f). The width W_(m) of the multi-layer glass melt is less than thewidth W_(f) of the float tank prior to the multi-layer glass meltentering the float tank. The multi-layer glass melt may flow over thesurface of the molten metal bath such that the width W_(m) of themulti-layer glass melt increases, the melt thickness T_(m) decreases,and the core to cladding thickness ratio T_(c):T_(cl) remains constantas the multi-layer glass melt solidifies into a laminated glass sheet.Various embodiments of methods for forming laminated glass sheets andapparatuses for performing the method will be described in more detailherein with specific reference to the appended drawings.

The term “liquidus viscosity,” as used herein, refers to the shearviscosity of the glass composition at its liquidus temperature.

The term “liquidus temperature,” as used herein, refers to the highesttemperature at which devitrification occurs in the glass composition.

The term “CTE,” as used herein, refers to the coefficient of thermalexpansion of the glass composition averaged over a temperature rangefrom about 20° C. to about 300° C.

Strengthened laminated glass articles may be formed by fusing one ormore glass cladding layers having a relatively low average coefficientof thermal expansion to a glass core layer which has a relatively highaverage coefficient of thermal expansion. As the laminated structurecools, the differences in the coefficients of thermal expansion of theglass core layer and the glass cladding layer create compressivestresses in the glass cladding layers.

Laminated glass sheets have been formed by a fusion lamination process,such as the fusion lamination process disclosed in U.S. Pat. No.4,214,886 and similar fusion lamination processes. Glass compositionsused in conjunction with fusion lamination processes generally have ahigh liquidus viscosity of greater than 100 kpoise such that the glassis able to be drawn vertically downward at elevated temperatures. Incomparison, glasses with lower viscosities tend to “run” at thetemperature of the fusion lamination process making it difficult to drawsuch glass compositions at elevated temperatures. Further, it has beenfound that reducing the temperature of the fusion lamination process toaccommodate glasses with lower viscosities (i.e., increasing theviscosity of the glass by lowering the processing temperatures) mayincrease the number of defects in the glass as the lower temperaturesencourage the nucleation and growth of crystals on the ceramic formingequipment of the fusion apparatus which can become dislodged andembedded in the glass. In addition, the shear mass of the fusion formingequipment, such as the isopipe, used in fusion forming processes makesit difficult to scale the processes to form large-width glass sheets.The methods and apparatuses described herein enable the formation oflaminated glass sheets from glass compositions with low liquidusviscosities and also enable the formation of large-width laminated glasssheets.

Referring now to FIG. 1A, an exemplary glass manufacturing apparatus 100for forming laminated glass sheets from molten glass is schematicallydepicted. The glass manufacturing apparatus generally comprises a coreglass delivery system 110, a cladding glass delivery system 120, a slotdraw apparatus 140, and a float tank 160. The float tank contains amolten metal bath 162, such as molten tin or the like.

The core glass delivery system 110 generally includes a core meltingvessel 101, a core fining vessel 103, a core mixing vessel 104, a coredelivery vessel 108, and a core feed pipe 109 coupled to a core slot ofthe slot draw apparatus 140. The cladding glass delivery system 120generally includes a cladding melting vessel 121, a cladding finingvessel 123, a cladding mixing vessel 124, a cladding delivery vessel128, and a cladding feed pipe 129 coupled to at least one cladding slotof the slot draw apparatus 140.

The float tank 160 is generally positioned below the core glass deliverysystem 110 and the cladding glass delivery system 120 such that moltencore glass 106 and molten cladding glass 126 can be delivered to thefloat tank by gravity. In the embodiment of the float tank 160 depictedin FIG. 1A, the float tank 160 includes a receiving plane 161 suspendedover the surface of the molten metal bath 162. The receiving plane 161includes a receiving surface 163 for receiving a multi-layer glass melt300 discharged from the slot draw apparatus 140. The receiving surface163 is positioned at an angle with respect to the surface of the moltenmetal bath 162 such that the multi-layer glass melt discharged from theslot draw apparatus 140 flows over the receiving surface 163 and ontothe surface of the molten metal bath 162 in a controlled manner.

While the float tank 160 of FIG. 1A is depicted with a receiving plane161 having a receiving surface 163, it should be understood that, inother embodiments (not shown), the float tank 160 may be constructedwithout a receiving plane 161. In these embodiments, the multi-layerglass melt discharged from the slot draw apparatus 140 may be depositeddirectly on the surface of the molten metal bath 162.

Referring to FIGS. 1A and 2, in some embodiments, the float tank 160 mayalso include one or more top rolls 170 (one depicted in FIG. 1A) forcontacting the multi-layer glass melt 180 as it flows over the surfaceof the molten metal bath 162. The top rolls 170 are each coupled to arotating shaft 171 such that, as the top rolls rotate, the multi-layerglass melt is drawn in a direction of the width W_(f) of the float tank160 and/or a length L_(f) of the float tank 160 to encourage the glassmelt to spread over the surface of the molten metal bath 162.

Referring to FIGS. 1A-1B and 3-4, the slot draw apparatus 140 isdisposed over the float tank 160 and oriented such that a slot angle θbetween the slot draw apparatus 140 and the surface of the molten metalbath 162 is greater than or equal to 0° and less than 90°. The slot drawapparatus is formed from a precious metal, such as platinum, platinumalloys or other precious metals suitable for use at the elevatedtemperatures of a glass forming process. The slot draw apparatus 140generally comprises a core slot 142 and at least one cladding slot whichis substantially parallel with the core slot 142. The width W_(s) of theslot draw apparatus 144 (i.e., the width of the core slot 142 and thewidth of the cladding slot(s) 144) is less than the width of the floattank 160 (see, e.g., FIG. 2).

In the embodiment of the slot draw apparatus 140 shown in FIGS. 1A-1Band 3-4, the slot draw apparatus is constructed with a first claddingslot 144 a positioned over the core slot 142 and a second cladding slot144 b positioned beneath the core slot 142. In this embodiment, the slotdraw apparatus 140 may be used to produce a multi-layer glass melt witha central core disposed between two cladding layers. However, it shouldbe understood that the slot draw apparatus 140 may be constructed with asingle cladding slot positioned either over the core slot 142 or belowthe core slot 142, such as when the slot draw apparatus is 140 is usedto form a multi-layer glass melt with a single core layer and a singlecladding layer. Further, it should also be understood that the slot drawapparatus may be formed with greater than three slots, such as when theslot draw apparatus is used to form a multi-layer glass melt with morethan three layers.

The core slot 142 of the slot draw apparatus 140 has a core height H_(c)and the at least one cladding slot has a height H_(cl). In embodimentswhere the slot draw apparatus contains a first cladding slot 144 a and asecond cladding slot 144 b, as depicted in FIGS. 3 and 4, the firstcladding slot may have a height H_(cla) and the second cladding slot mayhave a height H_(clb). In some embodiments, the height H_(c) of the coreslot may be equal to the height of each of the cladding slots. In otherembodiments, the height H_(c) of the core slot may be different than theheight of the cladding slots. In still other embodiments, the heightH_(cla) of the first cladding slot 144 a may be different than theheight H_(clb) of the second cladding slot.

In the embodiment of the slot draw apparatus 140 shown in FIGS. 3-4, thecore feed pipe 109 is coupled to the core slot 142 of the slot drawapparatus 140, as depicted in FIG. 4, such that molten core glassdelivered to the slot draw apparatus 140 with the core feed pipe 109flows through the core slot 142. The cladding feed pipe 129 is coupledto the first cladding slot 144 a and the second cladding slot 144 b withfeed plenums 145 a, 145 b, respectively. Accordingly, the moltencladding glass delivered to the slot draw apparatus 140 through thecladding feed pipe 129 flows through the plenums 145 a, 145 b andthrough the first cladding slot 144 a and the second cladding slot 144b, respectively.

In general, the pressure drop of the molten glass flowing through theslots is greater than the pressure drop of the molten glass in therespective feed pipes. For example, in some embodiments, the pressuredrop of the molten glass through the slot draw apparatus is at least 10×greater than the pressure drop of the molten glass in the correspondingfeed pipe. This pressure drop in the slot draw apparatus 140 encouragesthe molten glass to fill each of the slots across the entire width W_(s)of the slot draw apparatus 140 thereby promoting uniformity in themulti-layer glass melt formed by the slot draw apparatus.

Despite being formed from metals and/or alloys suitable for use at hightemperatures, the dimensions of the slot draw apparatus 140 may changeover time due to elevated temperature exposure. In order to minimizedistortions in the resultant multi-layer glass melt, the core slot 142and the cladding slots 144 a, 144 b of the slot draw apparatus mayinclude a plurality of reinforcing webs 147 positioned in each of theslots, as depicted in FIGS. 3-4. The reinforcing webs improve themechanical rigidity of the slot draw apparatus and also minimizedimensional changes in the slot draw apparatus due to prolonged elevatedtemperature exposure.

In some embodiments of the slot draw apparatus 140, the reinforcing webs147 are recessed from the slot openings, as depicted in FIG. 4. Thisconfiguration allows the molten glass to flow around the webs andre-knit into a continuous mass prior to exiting each of the slots. Theprocess of re-knitting the glass web generally occurs between the end ofthe reinforcing webs 147 and the exit of the slot draw apparatus 140 andis assisted by the pressure drop in this portion of the slot drawapparatus as well as the surface tension of the molten glass. There-knitting process may be further assisted by the specific geometry ofthe webs as well as gravity as the molten glass exits the slot drawapparatus and is deposited in the molten metal bath. However, in otherembodiments (not shown), the reinforcing webs 147 may extend to the slotopening.

While FIGS. 3-4 schematically depicts a slot draw apparatus 140 whichincludes reinforcing webs 147 in each of the slots, it should beunderstood that the reinforcing webs are optional and that, in someembodiments, the slot draw apparatus 140 may be formed withoutreinforcing webs.

Referring again to FIGS. 1A and 2, in operation, core glass batchmaterials are introduced into the core melting vessel 101 as indicatedby arrow 102. The core glass batch materials are melted in the coremelting vessel 101 to form molten core glass 106. The molten core glass106 flows into the core fining vessel 103 which has a high temperatureprocessing area that receives the molten core glass 106 from the coremelting vessel 101. The core fining vessel 103 removes bubbles from themolten core glass 106. The core fining vessel 103 is fluidly coupled tothe core mixing vessel 104 by a connecting tube 105. That is, moltenglass flowing from the core fining vessel 103 to the core mixing vessel104 flows through the core connecting tube 105. The core mixing vessel104 is, in turn, fluidly coupled to the core delivery vessel 108 by aconnecting tube 107 such that molten glass flowing from the core mixingvessel 104 to the core delivery vessel 108 flows through the connectingtube 107. The core delivery vessel 108 supplies the molten core glass106 to the core slot of the slot draw apparatus 140.

Simultaneously, cladding glass batch materials are introduced into thecladding melting vessel 121 as indicated by arrow 122. The claddingglass batch materials are melted in the cladding melting vessel 121 toform molten cladding glass 126. The cladding fining vessel 123 has ahigh temperature processing area that receives the molten cladding glass126 from the cladding melting vessel 121. The cladding fining vessel 123removes bubbles from the molten cladding glass 126. The cladding finingvessel 123 is fluidly coupled to the cladding mixing vessel 124 by aconnecting tube 125. That is, molten cladding glass flowing from thecladding fining vessel 123 to the cladding mixing vessel 124 flowsthrough the cladding connecting tube 125. The cladding mixing vessel 124is, in turn, fluidly coupled to the cladding delivery vessel 128 by aconnecting tube 127 such that molten glass flowing from the claddingmixing vessel 124 to the cladding delivery vessel 128 flows through theconnecting tube 127. The cladding delivery vessel 128 supplies themolten cladding glass 126 to at least one cladding slot of the slot drawapparatus 140.

The molten core glass and the molten cladding glass flow through theslot draw apparatus 140 in the respective core and cladding slots. Therelative orientation of the slots in the slot draw apparatus 140 causesthe molten core glass and the molten cladding glass to be layeredtogether upon exiting the slot draw apparatus 140, thereby forming amulti-layer glass melt 300, such as the multi-layer glass melt 300depicted in cross section in FIG. 5. The multi-layer glass melt 300discharged from the slot draw apparatus has a melt thickness T_(m) andincludes a core layer 302 disposed between a first cladding layer 304 aand a second cladding layer 304 b. The core layer 302 has a thicknessT_(c), the first cladding layer 304 a has a thickness T_(cla) and thesecond cladding layer 304 b has a thickness T_(clb). The thickness ofeach of these layers is generally proportional to the cube of the heightof the corresponding slot (i.e., the core layer 302 has a thicknessT_(c)≈H_(c) ^(a), the first cladding layer 304 a has a thicknessT_(cla)≈H_(cla) ³, and the second cladding layer 304 b has a thicknessT_(clb)≈H_(clb) ³). Further, the multi-layer glass melt 300 has a coreto cladding thickness ratio T_(c):T_(cl) where T_(c) is the thickness ofthe core layer 302 and T_(cl) is the sum of the thicknesses of thecladding layers 304 a, 304 b. Accordingly, in embodiments in which twocladding slots are disposed on either side of a core slot, the core tocladding thickness ratio Tc:Tcl of the multi-layer glass melt 300 can beapproximated by the equation H_(c) ³/(H_(cla) ³+H_(clb) ³). The widthW_(m) of the multi-layer glass melt 300 is generally the same as thewidth W_(s) of the slot draw apparatus 140 as the core layer 302 and thecladding layers 304 a, 304 b are discharged from the slot drawapparatus. Accordingly, it should be understood that the width W_(m) ofthe multi-layer glass melt 300 is generally less than the width of thefloat tank W_(f) prior to the multi-layer glass melt 300 entering thefloat tank 160.

In the embodiment of the glass manufacturing apparatus 100 depicted inFIG. 1A, the slot draw apparatus 140 is oriented at a slot angle greaterthan or equal to about 0 degrees and less than 90 degrees relative tothe surface of the molten metal bath to facilitate depositing themulti-layer glass melt 300 onto the surface of the molten metal bath 162while still maintaining the orientation and integrity of the layeredstructure imparted to the multi-layer glass melt 300 by the slot drawapparatus 140. Further, the non-perpendicular orientation of the slotdraw apparatus 140 with respect to the surface of the molten metal bathencourages the multi-layer glass melt 300 to flow over the surface ofthe molten metal bath 162 in a direction away from the slot drawapparatus 140.

As noted above, the embodiment of the float tank 160 depicted in FIG. 1Aincludes a receiving plane 161 suspended over the surface of the moltenmetal bath 162. The receiving plane 161 includes a receiving surface 163which is angled downward, into the molten metal bath 162. In thisembodiment, the multi-layer glass melt 300 discharged from the slot isdeposited on to the receiving surface 163 of the receiving plane 161 inorder to introduce the multi-layer glass melt 300 into the molten metalbath 162 in a controlled manner. Specifically, the multi-layer glassmelt 300 is discharged from the slot draw apparatus 140 onto thereceiving surface 163 such that the multi-layer glass melt 300 flowsover the receiving surface 163 and onto the surface of the molten metalbath 162, thereby maintaining the orientation and integrity of theindividual layers of the multi-layer glass melt 300.

While FIG. 1A depicts the multi-layer glass melt 300 as being depositedon the receiving surface 163 of the receiving plane 161 before enteringthe molten metal bath 162, it should be understood that this step isoptional. For example, in some embodiments (not shown) the multi-layerglass melt 300 may be deposited directly into the molten metal bath 162without first being deposited onto the receiving surface 163 of areceiving plane 161 suspended over the molten metal bath 162.

Stiller referring to FIGS. 1A and 2, upon being deposited on the moltenmetal bath 162, the multi-layer glass melt 300 flows over the surface ofthe molten metal bath 162. As the multi-layer glass melt flows over thesurface of the molten metal bath 162, the multi-layer glass melt 300spreads over the surface of the molten metal bath 162 in the directionof both the length L_(f) and width W_(f) of the float tank 160 such thatthe width W_(m) of the multi-layer glass melt 300 increases and thethickness T_(m) of the multi-layer glass melt 300 decreases as themulti-layer glass melt reaches both an equilibrium width and anequilibrium thickness on the surface of the molten metal bath 162.However, while the melt thickness T_(m) of the multi-layer glass melt300 decreases and the width W_(m) of the multi-layer glass meltincreases, the core to cladding thickness ratio T_(c):T_(cl) remainsconstant as the multi-layer glass melt solidifies into a laminated glasssheet.

As noted hereinabove, the glass manufacturing apparatus 100 may includeone or more top rolls 170 which may be used to contact the multi-layerglass melt 300 and draw the multi-layer glass melt 300 over the surfaceof the molten metal bath 162, thinning the multi-layer glass melt 300and, optionally, increasing the width W_(m) of the multi-layer glassmelt 300. Accordingly, in some embodiments, the top rolls 170 may beused to draw the multi-layer glass melt 300 in a direction of the widthW_(f) of the float tank as the multi-layer glass melt flows over thesurface of the molten metal bath. In some other embodiments, the toprolls 170 may be used to draw the multi-layer glass melt 300 in adirection of the width W_(f) of the float tank and in a direction of thelength L_(f) of the float tank as the multi-layer glass melt 300 flowsover the surface of the molten metal bath 162.

As the multi-layer glass melt flows and/or is drawn over the surface ofthe molten metal bath 162, the multi-layer glass melt 300 graduallycools and solidifies, forming a laminated glass sheet. In someembodiments described herein, the cladding glass has a first glasscomposition which has an average cladding coefficient of thermalexpansion CTE_(clad) and the core glass is formed from a second,different glass composition which has an average coefficient of thermalexpansion CTE_(core). In these embodiments, the CTE_(core) may begreater than the CTE_(clad) such that, when the multi-layer glass melt300 solidifies, the difference in the coefficients of thermal expansionresults in the cladding glass being compressively stressed therebyincreasing the mechanical strength of the laminated glass sheet withoutthe glass sheet being ion exchanged or thermally tempered.

The methods and apparatuses described herein may be used to producelaminated glass sheets of varying thicknesses and widths. In particular,the methods and apparatuses described herein may be scaled to producelaminated glass sheets having widths on the order of several meters. Forexample, in some embodiments, the width of the resultant glass sheet maybe greater than 1 meter or even greater than 3 meters. In someembodiments, the width of the resultant glass sheet may be greater than4 meters or even greater than 5 meters.

Further, the thicknesses of the resultant laminated glass sheets may beless than 1 cm. For example, in some embodiments, the thickness of theresultant laminated glass sheet may be less than or equal to 7 mm oreven less than or equal to 5 mm. In some embodiments, the thickness ofthe resultant laminated glass sheet may be less than or equal to 2.5 mm.In still other embodiments the thickness of the resultant laminatedglass sheet may be less than or equal to 1 mm.

Further, the methods and apparatuses described herein may also be usedto form laminated glass sheets with different structures. For example,any number of cladding slots may be added on either side of the coreslot in order to produce a laminated glass sheet having the desiredstructure. The methods and apparatuses described herein may be used toproduce laminated glass sheets with symmetrical claddings (i.e., thesame number of cladding layers on either side of the glass core) orasymmetrical claddings (i.e., a different number of cladding layers oneither side of the glass core). Further, the methods and apparatusesdescribed herein may also be used to produce laminated glass sheetswherein the thicknesses of the cladding layers are symmetrical orasymmetrical about the glass core.

While the methods and apparatuses described herein are compatible withglass compositions of varying liquidus viscosities, the methods andapparatuses described herein are particularly well suited for use withcore glass compositions and cladding glass compositions which have lowerliquidus viscosities which are not generally suitable for use withfusion forming processes such as fusion lamination processes. Forexample, in the embodiments described herein, the core glasscompositions and the cladding glass compositions may have liquidusviscosities less than 100 kpoise. In some embodiments, the core glasscompositions and the cladding glass compositions may have liquidusviscosities less than or equal to 100 kpoise, or even less than or equalto 50 kpoise. In some embodiments, the core glass compositions and thecladding glass compositions may have liquidus viscosities less than orequal to 30 kpoise or even less than or equal to 20 kpoise.

EXAMPLES

The methods and apparatuses will be further clarified by the followinghypothetical example.

Example 1

While not wishing to be bound by theory, it is believed that the methodsand apparatuses described herein may be used to form laminated glasssheets as exemplified by the following hypothetical example. Thehypothetical slot draw apparatus has a core slot disposed between afirst cladding slot and a second cladding slot. The core slot had aheight H_(c) of 0.0125 m. The cladding slots each had a heightH_(cla)=H_(clb)=0.006 m. The hypothetical slot draw apparatus had awidth W_(s) of 0.4 m. Based on the foregoing, the core to cladding ratioT_(c):T_(cl) of the glass melt discharged from the slot draw apparatusis 4.5. In this hypothetical, the slot draw apparatus may be coupled toa core glass delivery system and a cladding glass delivery system which,combined, are capable of delivering 37 metric tons of glass per day tothe slot draw apparatus. The core glass and the cladding glasscompositions hypothetically have identical viscosities and thetemperature of the glass manufacturing system is maintained at atemperature such that both the core glass and the cladding glass haveviscosities of 2000 poise. It is believed that the glass manufacturingsystem of this hypothetical example is suitable for forming a glasssheet having a width of 4 m or greater.

It should now be understood that the methods and apparatuses describedherein may be utilized to produce laminate glass sheets from core andcladding glass compositions having a broad range of liquidusviscosities, including liquidus viscosities of less than 100 kpoise oreven less than 20 kpoise. Further, the methods and apparatuses describedherein may be scaled to produce glass sheets having widths on the orderof several meters, including, without limitation, glass sheets withwidths greater than about 4 meters.

Further, the methods and apparatuses described herein may be utilizedduring formation of the glass sheet to produce a strengthened laminatedglass sheet and, as such, the need for secondary processing steps may beeliminated. Accordingly, the risk of damaging the glass sheet as theglass sheet is transferred to different processing areas may also beeliminated thereby decreasing production losses and production costs.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the embodiments describedherein without departing from the spirit and scope of the claimedsubject matter. Thus it is intended that the specification cover themodifications and variations of the various embodiments described hereinprovided such modification and variations come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method for forming a laminated glass sheet, themethod comprising: delivering a molten core glass and a molten claddingglass to a slot draw apparatus such that the molten core glass passesthrough a core slot of the slot draw apparatus and the molten claddingglass passes through at least one cladding slot of the slot drawapparatus to form a multi-layer glass melt with a width W_(m), a meltthickness T_(m), and a core to cladding thickness ratio T_(c):T_(cl)upon exiting the slot draw apparatus; directing the multi-layer glassmelt onto a surface of a molten metal bath with a width W_(f) that isgreater than the width W_(m) such that, as the multi-layer glass meltflows over the surface of the molten metal bath, the width W_(m) of themulti-layer glass melt increases, the melt thickness T_(m) decreases,and the core to cladding thickness ratio T_(c):T_(cl) remains constantas the multi-layer glass melt solidifies into the laminated glass sheet.2. The method of claim 1, further comprising directing the multi-layerglass melt onto a receiving surface of a receiving plane prior todirecting the multi-layer glass melt onto the surface of the moltenmetal bath.
 3. The method of claim 2, wherein the receiving surface ofthe receiving plane is oriented at a receiving plane angle greater thanor equal to 0° and less than 90° with respect to the surface of themolten metal bath.
 4. The method of claim 1, further comprising:contacting an upper surface of the multi-layer glass melt with aplurality of top rollers when the multi-layer glass melt is on thesurface of the molten metal bath; and drawing the multi-layer glass meltin a direction of the width W_(f) of the molten metal bath with theplurality of top rollers.
 5. The method of claim 1, further comprising:contacting an upper surface of the multi-layer glass melt with aplurality of top rollers when the multi-layer glass melt is on thesurface of the molten metal bath; and drawing the multi-layer glass meltin a direction of the width W_(f) and a length L_(f) of the molten metalbath with the plurality of top rollers.
 6. The method of claim 1,wherein the core slot has a core height H_(c), the at least one claddingslot has a cladding height H_(cl) and the core height H_(c) is not equalto the cladding height H_(cl).
 7. The method of claim 1, wherein the atleast one cladding slot comprises a first cladding slot and a secondcladding slot and the core slot is positioned between the first claddingslot and the second cladding slot.
 8. The method of claim 7, wherein thefirst cladding slot has a first height H_(cla), the second cladding slothas a second height H_(clb), and the first height H_(cla) is not equalto the second height H_(clb).
 9. The method of claim 7, wherein the coreslot has a core height H_(c), the first cladding slot has a first heightH_(cla), the second cladding slot has a second height H_(clb), and thecore height H_(c) is greater than each of the first height H_(cla) andthe second height H_(clb).
 10. The method of claim 1, wherein the coreslot and the at least one cladding slot comprise a plurality ofreinforcing webs.
 11. The method of claim 10, wherein the reinforcingwebs are recessed from an outlet of the slot draw apparatus.
 12. Themethod of claim 1, wherein the core slot and the at least one claddingslot are oriented in parallel with one another.
 13. The method of claim1, wherein the slot draw apparatus is oriented at a slot angle greaterthan or equal to 0° and less than 90° with respect to the surface of themolten metal bath.
 14. The method of claim 1, wherein a width W_(s) ofthe slot draw apparatus is less than the width W_(f) of the molten metalbath.
 15. The method of claim 1 wherein the laminated glass sheet has awidth greater than 4 meters.
 16. An apparatus for forming a laminatedglass sheet, the apparatus comprising: a core glass melting vessel; acladding glass melting vessel; a float tank having a width W_(f); and aslot draw apparatus positioned over the float tank to deliver amulti-layer glass melt comprising a molten core glass and a moltencladding glass to the float tank, the slot draw apparatus having a widthW_(s) less than the width W_(f) of the float tank and comprising a coreglass slot and at least one cladding glass slot, the core glass slotfluidly coupled to the core glass melting vessel to receive the moltencore glass, and the at least one cladding glass slot fluidly coupled tothe cladding glass melting vessel to receive the molten cladding glass.17. The apparatus of claim 16, further comprising a receiving planepositioned between the slot draw apparatus and the float tank to receivethe multi-layer glass melt discharged from the slot draw apparatus. 18.The apparatus of claim 16, wherein the slot draw apparatus is orientedat a slot angle greater than or equal to 0° and less than 90° withrespect to a surface of a molten metal bath contained in the float tank.19. The apparatus of claim 16, wherein: the at least one cladding slotcomprises a first cladding slot having a first height H_(cla) and asecond cladding slot having a second height H_(clb) that is not equal tothe first height H_(cla); and the core slot is positioned between thefirst cladding slot and the second cladding slot.
 20. The apparatus ofclaim 16, further comprising a plurality of top rollers to contact themulti-layer glass melt in the float tank and draw the multi-layer glassmelt in a direction of the width W_(f) of the float tank and increasethe width W_(m) of the multi-layer glass melt.